The long term goal of this research program is to determine how the brain regulates reproductive behavior. The laboratory rat will be used as the model system for this work because the extensive work that has been done on this species makes it a valuable tool. Reproductive behavior is regulated by gonadal hormones which act within specific brain sites to bring about the behaviors that are required to maximize its reproductive potential. The experiments in this proposal focus on the biochemical and endocrinological events that must occur in these specific brain sites to translate the hormonal message into the program of integrated neural activity. Much of the proposed work is concerned with the effects of estrogen upon processes that regulate acetycholine action in the hypothalamus and midbrain. It would appear that estrogen is capable of modifying cholinergic activity in extensive brain regions, many of which have long been associated with emotionality as well as reproductive behavior. A better understanding of these basic neuroendocrine and biochemical brain processes will provide insight into many areas related to health including reproduction, emotionality and behavioral fluctuations that are associated with variations in gonadal hormones.